1. Field of the Invention
The invention is directed to a method for adapting the stimulation frequency of a heart pacemaker to the burden of a patient, whereby a characteristics regulator controls the stimulation frequency dependent on a burden-dependent regulating variable and whereby, by changing the stimulation frequency during defined time intervals, an identification is made to see whether a measured value dependent on the cardiac minute output thereby changes, and whereby an optimization controller influences a characteristic that represents the relationship between the regulating variable and the stimulation frequency which correspondingly influences this change in measured value.
2. Description of the Prior Art
A method of this species is disclosed by EP-A-2 0 165 566. The stimulation frequency of a heart pacemaker is thereby regulated dependent on the central venous blood oxygen saturation in the heart. The central venous blood oxygen saturation is calculated according to the principle of reflection oximetry that, for example, is disclosed in detail in DE-A-31 52 963.
An optimum adaptation to the individual hemodynamic situation of the patient that changes over time is not possible with a permanently prescribed, invariable characteristic such as the relationship between blood oxygen saturation and stimulation frequency. In the EP-A2-0 165 566, an optimizing control that acts continuously in addition to the characteristics control is thereby provided. The optimizing control continuously monitors the tendency of the value of the blood oxygen saturation and, by automatic elevation or lowering of the frequency, determines whether an improvement (measured value increase) of the value of the blood oxygen saturation ensues or not. It is not only one defined characteristic but an entire family of characteristics that is now allocated to every value of blood oxygen saturation.
This arrangement, however, has the disadvantage that it makes a decision after every change in frequency whether a positive or negative reaction of the blood oxygen saturation ensued and, thus, there is the risk of incorrect decision as a consequence of disturbing changes of the oxygen saturation that are dependent on burden above all.